Apparatus and method for vibration sealing

(24) Course day (62) Number of the application (86) International filing day (86) Filing date for the European patent application (30)

83-12-12 (11) Publication number 430 775

77-07-29

7 01 27 Angola income as:

77-01-27

EJ Swedish patent application

O completed international patent application with number

O converted European patent application with number

76-01-28 US 652916?

(71) Applicant: Ex-Cell-0 Corporation, Troy Mich US (72) Inventor: ER Bosch, Earl W Walke Jr., Plymouth, Wixom

Mich (74) Representative: AWAPATENT AB (54) Title: Methods and apparatus for sealing thermoplastic coated cardboard boxes (56) Published publications: US 3,905,280 (93-44.1), US 3,499,808 (156-73)

IN

770(18.50-6

The present invention relates generally to a method and apparatus for packaging, and more particularly to an improved method and apparatus for sealing cartons or containers of thermoplastic coated cardboard.

A particular object of the invention is to seal cardboard boxes or containers of cardboard, which are coated on both sides with a thermoplastic material such as polyethylene. The thermoplastic coating on the board is not only used as a moisture-proof material but also serves as a heat and pressure sensitive adhesive which, when sealing the closure elements on the container, makes this fluid tight, when filled with milk or other contents, sealed and sealed. Examples of a container of this type are shown and described in U.S. Patents 3,120,089 and 3,910,014.

Heretofore, thermoplastic-coated cardboard boxes have been sealed by contacting the layers of the end closure means of the container, whereupon heat is applied to activate the thermoplastic coating so that it flows to the portions to be joined and sealed. As the thermoplastic material cools and solidifies, the layers are sealed and glued together. In addition to requiring complicated and expensive apparatus to provide the considerable amount of energy required, complicated apparatus is also required.

7700850-6 methods and systems for diverting the heat from, the place at which the packaging operation is performed. Examples of this general type of apparatus are shown and described in U.S. Patent Nos. 3,002,328; 3,120,089, 3,166,994, 3,187,647, 3,239,995 and 3,309,841.

U.S. Patent Nos. 3,905,280 and 3,910,014 disclose an apparatus for sealing the ends of thermoplastic-coated cardboard containers by vibration welding, converting mechanical energy to localized thermal energy to reduce the required amount of heat and energy and eliminate the need for expensive systems and methods. release of the excess heat. US Patent 3,526,792 relates to an ultrasonic converter having a conversion device for converting electrical energy into mechanical energy and a concentration horn for concentrating the mechanical energy into vibrations of the desired frequency. According to the aforementioned US patents 3 905 280 and 3 910 014, the horn of the vibration welding apparatus vibrates at a predetermined frequency upon activation and cooperates with a counter hold to clamp the layers of the thermoplastic coated board between the working surface of the horn and a support surface of the counter hold. As the thermoplastic-coated cardboard layers are squeezed between the working surfaces of the horns and counterstops, the vibration of the horn produces frictional heat sufficient to activate the thermoplastic coatings of the layers so that the layers of the thermoplastic material flow together. When the vibration is terminated, the thermoplastic will cool and solidify for sealing the layers and securing them throughout the entire area of ​​the closure. Among the advantages of using vibration welding may be mentioned that the heat generated by the vibration of the horn is concentrated in the sealed area and little, if any, excess heat is required to carry out the sealing operation.

Two steps occur when sealing thermoplastic coated cardboard containers by vibration welding. These steps consist of 1) ·. the activation stage, during which the friction of the vibration horn generates enough heat to activate the thermoplastic coating so that it begins to flow and 2) the cooling step, during which the layers are maintained squeezed between the horn and the antler with the horn deactivated to allow the previously activated thermoplastic coating to for forming the seal. Thus, a complete cycle of sealing layers of thermoplastic-coated cardboard includes 1) placement of the working surfaces on the abutments and horns opposite

7700850-6 to each other on each side of the sealing layers,

2) activating the thermoplastic coating of the layers between the working surfaces by means of frictional heat to bring the layers together, 3) cooling and curing the previously activated thermoplastic material while still retaining between the working surfaces of the counter and the deactivated horn, and 4) separating the working surfaces the abutment and the horn in and for removing the cardboard layers after the sealing is achieved. The time required to accomplish this during each cycle has been of the order of 1/2 to 2 seconds, depending on the thickness of the paperboard, the thickness of the thermoplastic coating, the number of layers and the surface area to be sealed.

In vibration welding of this type, it has been customary to actuate the horn with pressure to initiate the horn vibration, that is, the working surface of the horn has been brought into contact with the layers intended for welding and the horn has begun to vibrate when a predetermined pressure on the horn's working surface is sensed by horn actuators.

The pressure on the entire sealing surface must be maintained within predetermined limits. If the pressure is too low, the friction between the vibrating horn and the cardboard layers will be insufficient to generate enough heat to activate the thermoplastic coating. If the pressure is too high, burning occurs, ie the thermoplastic coating is removed at high pressure points, thereby destroying the seal.

Another problem that can arise when an excessive clamping pressure occurs between the horn and the counter is that the vibration can be transmitted to the counter. If this occurs, the friction between the horn and the cardboard layers is reduced due to the resulting reduction of relative movement between the vibrating horn and the layers. In other words, the excessive pressure will cause a vibration of the abutment with the horn, so that the cardboard layers tend to move together with the horn instead of frictionally counteracting the vibrating horn. The friction reduction reduces the possibility of sufficient heat being generated to activate the thermoplastic or at least extend the time required to activate the thermoplastic coating. The likelihood of this happening increases as the mass of the opponent increases. A counterweight with low mass relative to the horn has a greater tendency to start vibrating than is the case if the counterweight has a relatively large mass.

A significant factor in determining the production rate

7700850-6 is the time required for the sealing operation, which, as indicated above, includes both activation and cooling. When a carton is in the welding station and the sealing layers are squeezed between horns and counterions, the inadvertent cooling time after deactivation of the horn increases with the layers remaining squeezed between the horn and counterweight, the probability of the layers breaking apart before thermoplastic coating. prevent the closure. In high speed packaging systems, the available time for the sealing operation is determined by the speed at which the cartons must pass the welding cycle, by the speed of other machines throughout the system. For example, the welding apparatus must be accommodated in a system which includes machines for feeding and erecting cartons from a flat blank, such as machines of the kind further described in U.S. Patent Nos. 3 599 541 and 3 937 131, while the filling and sealing apparatus is of the kind disclosed and described in U.S. Patent No. 3,910,014.

It is an object of the present invention to increase the rate of production of systems for forming, filling and sealing cartons of thermoplastic coated cardboard by vibrating welding of cardboard ends to form a seal by reducing the time required to activate the thermoplastic material during the sealing operation.

It is a further object of the invention to provide an improved method and apparatus for providing a seal between a plurality of layers of thermoplastic-coated board, wherein different numbers of layers exist at different locations of the area to be sealed, so that thickness variations of the sealing area occur. time, required to activate the thermoplastic coating during the vibration welding step during the sealing operation is reduced to provide an extended cooling time · during the sealing operation and to reduce the likelihood that the layers will disintegrate as the clamp between the horn and counterbeam surfaces of the vibration welding apparatus ceases.

The object of the invention is achieved by the method and apparatus for carrying out this method, as defined in the following claims.

The invention will now be described in more detail with reference to the accompanying drawings, which show exemplary embodiments. Fig. 1 shows schematically an embodiment of an apparatus according to the above

No. 7700850-6 with the end of the end of a container made of thermoplastic-coated cardboard, which is illustrated in cross-section and arranged for sealing by the apparatus. Fig. 2 schematically shows another embodiment of the apparatus according to the invention with a flat end portion of a container which is shown in cross-section and is intended to be sealed by the apparatus. Fig. 3 schematically shows another embodiment of the invention with the upper end of a container of thermoplastic-coated cardboard placed for sealing by the apparatus, and Fig. 4 schematically shows another embodiment of the apparatus according to the invention with a flat end portion of a thermoplastic-coated cardboard container arranged for sealing. by means of the apparatus according to the invention.

In Fig. 1, an apparatus according to the invention is indicated for sealing a gable upper end 12 on a thermoplastic-coated cardboard box C. The cardboard end 12 has outer layer 14 of thermoplastic-coated cardboard which engages with one another adjacent the top portion of the cardboard as well as inner layer 16 of thermoplastic-coated cardboard between the outer layers below the top end. The apparatus 10 has a vibrating horn 18 and an abutment 20. The horn 18 is mounted on a vibrator 22 which is slidably mounted in a fixed cylinder 24 for movement to the left and right of FIG. 1. The bracket 20 is likewise mounted in a fixed cylinder 26 for displacement left and right; The horn 18 has a substantially flat work surface 28, which is opposite to a substantially flat work surface 30 on the abutment 20. When a carton top 12 is placed between the working surfaces 28 and 30, the counter and horn can be actuated to move towards one another in a sealing position, in which the surfaces 28 and 30 engage with opposite sides of the carton top during squeezing.

A control circuit 32 is schematically shown in Fig. 1 and is connected to the cylinder 24 by means of a conduit or other electrical conductor 34 so as to control the retraction and extension of the vibrator 22 in the cylinder. Similarly, the control circuit 32 is connected to the cylinder 26 by means of a line or other electrical conductor 36 for controlling retraction and extension of the counter 20 in the cylinder 26. A wire or other electrical conductor 38 also connects the control circuit to the vibrator 22 so as to initiate and stop its vibration.

The abutment 20 and the horn 18 may be located in a welding and sealing station through which a conveyor (not shown) for the carton C passes. Since a cardboard C is not located in the welding and

The closure station 7700850-6 resides with the retainer 20 and the horn 18 in their retracted positions, i.e., the retainer 20 is located in its far left position and the horn 18 is located in its far right position in FIG. Fig. 1 shows the position with the cardboard upper positioned between the opposite working surfaces 28 and 30, the control circuit 32 is activated. The control circuit 32 can be actuated by a switch or the like, which is positioned so that a carton can engage with it when it is displaced by the conveyor to the welding and closing station between the counter and the horn, for example as shown and described in US Patent 3,905,280. way.

When the control circuit 32 is actuated, the cylinders 24 and 26 are actuated to move the horn 18 and the counter 20 toward each other to the extended carton closing position. Before the horn 18 engages with the right outer thermoplastic coated cardboard layer 14, it is triggered, i.e., the vibrator 22 has been activated by the control circuit and in turn activates the horn and causes it to vibrate at a predetermined frequency (e.g. 20,000 Hz). Thus, the working surface 28 of the horn vibrates as it moves into engagement with the right cardboard layer 14. At the same time as the working surface 28 of the vibrating horn engages with the cardboard top 12, the working surface 30 of the abutment moves to engage the left outer outer cardboard layer 14. As the horn and counterbeam shift their respective working surfaces to clamping engagement with the cardboard layers of the cardboard top 12, the working surfaces 28 and 30 engage successively with the thicker, lower portion containing the layers 16, and then with the thinner upper portion containing only the layers 14. A higher squeezing pressure occurs in the thicker lower portion than in the thinner upper portion. Therefore, the minimum pressure required to produce sufficient friction is achieved to activate the thermoplastic coating first in the thicker portion and the thermoplastic in the thicker portion begins to flow before the thermoplastic in the thinner portion. As the pressure in the thinner upper portion, which contains only the layers 14, reaches the minimum value required to activate the thermoplastic, the clamping of the surfaces 28 and 30 stops against each other to prevent an excessive pressure in the thicker lower portion, which contains the inner layers 16. The control circuit 32 then deactivates the horn and stops its vibration. The abutment and the deactivated horn are then held in sealing position with the cardboard overlays sandwiched between surfaces 28 and 30 for a predetermined period of time to

7700850-6 allow cooling and solidification of the activated thermoplastic, thereby forming a seal between the top layer of the carton.

The aforementioned sequence of operations, which includes locking the horn 18 prior to its engagement with the cardboard layers in the top of the carton 12, reduces the time required per welding cycle to the order of 20-30 ms or by 10-15%, which is a significant increase in a mass production system.

As previously stated, the pressure must be maintained within predetermined limits beyond the entire sealing region, including with respect to Fig. 1, the lower thick portion having four layers 14 and 16, as well as the upper thin portion, which has only two layers 14. It has been found that the minimum pressure required to generate sufficient frictional heat to activate the thermoplastic coating is approximately 14.1 kg / cm, assuming the horn vibrates at a frequency of 20 kHz. At the same frequency it has been found that the maximum pressure must not exceed about 54.8 kg / cm. As according to Fig. 1, the working surfaces 28 and 30 are flat, the thickness of the paper must be such that it allows sufficient squeezing pressure between the surfaces 28 and 30 (ie at least 14.1 kg / cm) in the portion with the two layers with the pressure in the portion with the four the layers stand by

14.1-54.8 kg / cm. If the control circuit 32 prevents the clamping pressure from reaching the maximum pressure of 54.8 kg / cm, sealing will not occur in the part with the thin layers unless the pressure there reaches the minimum pressure of 14.1 kg / cm. Therefore, the permissible variation in thickness over the sealing area is such that it allows the clamping pressure between the surfaces 28 and 30 over the entire area to fall within the predetermined limits of about 14.1 kg / cm to about 54.8 kg / cm at a horn frequency of 20 kHz.

In the embodiment shown in Fig. 1, the thickness of each layer of cardboard is such that the difference in thickness between the two-layer portion and the four-layer portion allows a clamping pressure in both portions in the range between the predetermined minimum and maximum pressures found to be the above. about 14.1 kg / cm and

54.8 kg / cm as the horn vibrates at a frequency of 20 kHz.

Most thermoplastic-coated cardboard boxes are made of cardboard with a thickness of 0.3-0.7 mm and have a coating of polyethylene (or other thermoplastic material) with a thickness of 0.020-0.025 mm. As the thickness of the sealing layers increases, for example, because thicker cardboard is used and / or the number of layers abruptly changes, the squeeze pressure will increase and it becomes more difficult.

7700850-6 to maintain pressure between the planar work surfaces 28 and 30 within the required limits.

Referring to Fig. 1, it is assumed that the horn 18 vibrates at a frequency of 20 kHz upon activation, the thickness variation between the two layer portions of the top of the carton 12 containing only the layers 14, and the four-layer portion containing the layers 16 is sufficiently small. to allow the clamping pressure to fall within the range of 14.1-54.8 kg / cm.

Fig. 2 shows another embodiment of the apparatus according to the invention, which corresponds to the embodiment according to Fig. 1 and consequently has the same reference numerals but with the addition of a prime sign. In this embodiment 10 'of the apparatus, only the vibrator 22' and the vibrating horn 18 'carried therefrom are mounted for extension and retraction. The abutment 20 'is in the form of a mandrel and is mounted on a rotatable member 40' so as to support the bottom 42 'of a thermoplastic coated food board C of cardboard aligned with the horn. The cardboard bottom 42 'is conventionally manufactured by folding the sides of the board along notches and having inner layers 44' and overlapping outer layers 46 '. Thus, the cardboard bottom has three layers except where the outer layers overlap, where the number of layers is four.

The closure of the cardboard bottom 42 'takes place in the same manner as described with reference to Fig. 1 for closing the top end of the carton. The cylinder 24 'shifts the vibrator 22' and its horn 18 'upwardly towards the cardboard bottom from the retracted position shown. Before the horn's working surface 28 'engages the cardboard bottom, the control circuit 32' activates the vibrator 22 'for vibrating the horn. Thus, the opposite working surfaces 28 'and 30' of the horn and the abutment squeeze the layers 44 'and 46' of the carton, the cylinder 24 'exerting a force which puts all layers under pressure while maintaining the pressure within predetermined limits. The horn vibration activates the thermoplastic coating on the pressurized layers to float. The horn vibration is then terminated while retaining the cardboard bottom clamped so that the activated thermoplastic coating on the layers can cool and harden to form the seal between the layers. After the sealing is performed, the horn and vibrator are moved back to their retracted positions and the rotatable member 40 'is actuated to move the sealed cardboard bottom to a dispensing station and places another cardboard bottom to be sealed in front of the horn.

Fig. 3 shows an embodiment according to which the working surface of the counter support is stepped to accommodate variations in the thickness of the board top layer in the sealed area. Consequently, a greater layer thickness variation is possible while still maintaining the squeeze pressure in the range between the inner and maximum pressures.

In Fig. 3, the apparatus is generally denoted by 110. The parts corresponding to Fig. 1 have the same reference numerals increased by 100. The carton C has an upper portion 112, which is located between the working surfaces of a horn 118 and an opposing 112.

The working surface of the abutment 120 is stepped, as shown at 131, to accommodate the extra thickness of the layers 116 in the four-layer portion. Accordingly, the pressure is distributed more evenly over the two layers and the four layers of the cardboard top 112, with the horn 118 and the counter member 120 in the sealed position. A greater variation in thickness beyond the sealing area can be achieved by the apparatus of Fig. 3.

Fig. 4 shows an embodiment which corresponds to that of Fig. 2, except that the working surface of the abutment is stepped to accommodate variations in thickness. Parts, having the same reference numerals,

The working surface 130 of the counterbalance 120 ', a recess, as shown at 131' corresponding to those shown in FIG. 2, increased by 100.

is stepped or provided to accommodate the thickest portion of the overlapping layers 146 '.

The embodiments of Figures 3 and 4 act like those of Figures 2 and 2. As to Figures 3 and 4, it is obvious that the working surface of the horn may be stepped in place of the working surface of the abutment. Similarly, both workspaces can be stepped down, if desired.

The invention may not be considered limited to the embodiment described above and shown in the drawings can be modified within the scope of the following claims.

7700850-6